A support device of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 4,698,575. In this known support device, the force actuator system is provided with four rods acting as a parallelogram mechanism by which a rigidification member is coupled to a first bearing unit. A second bearing unit is directly fastened to the rigidification member, so that the object table is guided along a straight guide in an accurate manner. Displacements of the object table parallel to the z-direction of a few tens of micrometers are obtained by means of the force actuator system, the parallelogram mechanism preventing a tilting movement of the object table about an axis of rotation directed parallel to the base surface. The known support device is used inter alia in an optical lithographic device for the manufacture of integrated semiconductor circuits, the object table comprising a support surface for a semiconductor substrate to be illuminated. The semiconductor substrate is focused relative to a lens system of the optical lithographic device by a displacement parallel to the z-direction.
A drawback of the known support device, which becomes apparent upon the application of the support device in an optical lithographic device, is that focusing of a substrate takes place exclusively by means of a displacement of the substrate parallel to the z-direction. A substrate of non-uniform thickness is not optimally focused in this way. In addition, only comparatively small displacements of the substrate in the z-direction can be carried out by means of the known support device, because the rigidification member is directly fastened to the second bearing unit.